In the fabrication of light-emitting diodes, III-V group compound semiconductors, such as GaN, AlGaN, InGaN and AlInGaN, are common. Usually, epitaxial structures of most of the light-emitting devices made of the III-V group compound semiconductors are grown on an electrically insulating sapphire substrate, which is different from other light-emitting devices utilizing conductive substrates. The sapphire substrate is an insulator, so an electrode cannot be directly formed on the sapphire substrate. Electrodes have to be formed to be in contact respectively with a P-type semiconductor layer and an N-type semiconductor layer directly, so that the light-emitting devices of the aforementioned type can be completed.
Typically, a material of a growth substrate of a conventional light-emitting diode adopts N-type gallium arsenide (GaAs). The growth substrate composed of N-type GaAs can absorb light, so that most of the photons produced by the active layer of the light-emitting diode while being emitted towards the growth substrate are absorbed by the growth substrate, thus seriously affecting the light emitting efficiency of the light-emitting diode device.
In order to avoid the issue of light being absorbed by the substrate, I. Pollentirer et al. in the Gent university in Belgium disclosed a technology in the journal “Electronics Letters” about directly bonding the GaAs light-emitting diode wafer to the silicon (Si) substrate after the GaAs light-emitting diode wafer is stripped off the GaAs substrate in 1990. Additionally, the U.S. Pat. No. 5,376,580 (application date: Mar. 19, 1993) filed by Hewlett-Packard Co., U.S.A. disclosed a technology about directly bonding the AlGaAs light-emitting diode wafer to the other substrate after the AlGaAs light-emitting diode wafer is stripped off the GaAs substrate. However, the U.S. Pat. No. 5,376,580 has disadvantages of difficult process and low yield caused by the need to consider the consistency of the lattice direction between the bonding wafers, since the bonding mediums are semiconductors.